1. The Field of the Invention
This invention relates generally to the field of interleaver devices for use in optical networks. In particular, embodiments of the present invention relate to an improved interleaver device incorporating a laser bending calibration technique.
2. The Relevant Technology
Fiber optics are increasingly used for transmitting voice and data signals. As a transmission medium, light provides a number of advantages over conventional electrical communication techniques. For example, light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interference that would otherwise interfere with electrical signals. Light also provides a more secure signal because it does not emanate the type of high frequency components often experienced with conductor-based electrical signals. Light signals also can be conducted over greater distances without the signal loss typically associated with electrical signals on copper conductor.
Many conventional electrical networks are being upgraded to optical networks to take advantage of the increased speed and efficiency. One of the many required components of an optical network is an optical switching device. An optical switching device has the capability of switching an individual light signal between at least two different locations. Usually the optical signal is first demultiplexed or dispersed and the individual channels are switched and routed to specific locations. It is preferable to optically switch the optical signals rather than converting them to electrical signals and then switching them with conventional electrical switching techniques to maintain many of the advantages of optical networks.
The most common form of data transmissions within an optical network is wavelength division multiplexed (WDM) signals. A WDM signal is a single band of light that contains numerous different channels of information on its constituent wavelengths. For example, a particular band of light may have a wavelength range of 400 nanometers. This band of light can be broken up into numerous different subbands of smaller ranges of wavelengths. Each of these subbands can be referred to as an individual and distinct data channel, and generally do not interfere one with another. Therefore, one band of light can contain multiple independent data channels, each containing different data. Because of the demand for high bandwidth capabilities, there is an effort to increase the number of channels within a single band of light. This means that the subbands are compressed to smaller ranges of wavelengths, but still contain the same amount of information. This can lead to problems associated with separating or multiplexing the various channels for data processing.
In response to a demand for larger bandwidth capabilities, dense wavelength division multiplexing (DWDM) was developed. The term DWDM represents a standard of WDM in which the individual data channels are compressed together in a more dense configuration. For example, if a WDM signal has a 200 GHz channel spacing, a DWDM signal may have a 100 Ghz channel spacing. By decreasing the channel spacing, the overall bandwidth capabilities of a particular range of light are increased because more data channels could theoretically be included.
Because of the evolving channel spacing standards among optical signals, it has become more difficult to resolve or identify the individual channels within a very closely spaced optical signal. Therefore, a device is necessary that enables the spacing between the subbands or channels to be increased. An interleaver, or wavelength splitter, uses multiple interferometers to separate out the even and odd channels of a particular WDM signal into two output sets of channels, thereby enabling each of the two output sets of channels to have twice as much spacing between channels as the input set of channels. An interleaver is different from a multiplexer in that an interleaver does not separate individual channels, but rather simply increases the spacing between the channels such that they can more easily be processed. An interleaver can also be used to decrease the spacing between multiple channels by reversing the orientation of the interleaver device. This process of decreasing the spacing between the channels is generally referred to as deinterleaving. Interleavers and deinterleavers can also be used to increase and decrease the channel spacing in an optical signal such that various components that are configured to only work on a particular channel spacing can be utilized.
Optical interleavers must conform to very precise measurements to accurately increase the spacing evenly among the various channels and to ensure that particular channels are not cut off. If the resulting channel spacing is not even, data processing errors arise because specific channels are not be properly located. This effect is compounded by the number of channels in a single optical signal. For example, if a poorly calibrated interleaver device inconsistently separates the first few channels, all of the remaining channels will also be incorrectly positioned. Therefore, when a data processing device tries to obtain data from the various signals, it analyzes the wrong ranges of wavelengths, causing significant errors. In addition, it is possible for an interleaver device to cut off channels in the initial phase of separating out even and odd channels. For example, if the interleaver device is not properly calibrated to the spacing of the channels in the input signal, it may chop off signals, thinking it is separating between an even and an odd signal. Therefore, the calibration of an interleaver device is critical to its proper operation.
Optical interleavers have multiple variables or parameters which affect how the interleaver separates the even and odd channels in an optical signal. Depending on the type of optical interleaver, these parameters may include the length and angular relation of both the coupling layer and the cavity layers. In an interleaver utilizing two interferometers, the coupling layer is the spacing between the two interferometers. The coupling layer affects how the even and odd channels are separated into two different sets of channels. The cavity layer is the spacing between the mirrors in a Fabry-Perot style interferometer. The cavity layer in each of the interferometers affects how the two resulting sets of channels will be spaced.
Therefore, there is a need in the industry for an efficient method of manufacturing an interleaver device. The method should be cost effective, yet capable of manufacturing an interleaver consistent with extremely precise calibration measurements.